Self-centering compact damper unit applicable to structures for seismic energy dissipation

ABSTRACT

The damper unit  10  is applicable to structures for seismic energy dissipation. The damper unit  10  comprises, a lower beam  11,  an upper beam  12,  a left column  21,  a right column  22,  axially yielding dampers  41, 42  functioning as an energy dissipating means, a left post-tensioned steel bar  31,  and a right post-tensioned steel bar  32.  The left and right post-tensioned steel bars  31  and  32  are inserted in the left and right columns  21  and  22,  respectively. Upper ends of the steel bars  31  and  32  are connected with the upper beam  12.  Lower ends of the steel bars  31  and  32  are connected with the lower beam  11.  The columns  31  and  32  are semi-rigid connected with the upper beam  12  and the lower beam  11  by compressive forces generated from the steel bars  31  and  32.  Therefore, the damper unit  10  possesses both self-centering and seismic energy dissipation characteristics.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a self-centering compact damper unit applicable to structures for seismic energy dissipation.

2. Description of the Related Art

There have been developed various seismic resistant systems with using dampers, braces, and so on.

For example, Japanese Unexamined Patent Application Publication No. 2001-220709 (corresponding U.S. Pat. No. 6,722,088) discloses a seismic resistant frame structure comprising a pair of bridge columns, a beam, a pair of brace members, and a hysteretic damper (shear damper). The beam is supported by the columns. The damper is connected at a middle position of the beam. One end of each of the brace members is pin-connected at a middle position of each of the columns. The other end of each of the brace members is connected with the damper. The braces therefore form a reversed V shape.

Japanese Unexamined Patent Application Publication No. 2008-303686 discloses a shear panel damper and a structure to which the shear panel damper is applied. The shear panel damper is designed with the aim of easier replacement.

However, the structural members including dampers go into plastic state, and therefore, the residual displacement retains within the frame structure after major earthquakes. Accordingly, an adequate maintenance is necessary after major earthquakes for restoring the frame structure to return it to its original position and/or for replacing the damaged damper with a new one.

Japanese Unexamined Patent Application Publication No. 2008-297720 discloses a frame structure which constitutes a part of infrastructures such as an elevated highway bridge. The frame structure comprises a pair of bridge columns, a column supported beam, a pair of post-tensioned steel bars, and axially yielding dampers. The beam is semi-rigid connected with each of the columns. Each of the post-tensioned steel bars is inserted vertically through each of the columns. The axially yielding dampers are provided between the beam and each of the columns as well as between the each of the columns and the respective column base. A self-centering mechanism is developed within the frame structure by means of the post-tensioned steel bars. Accordingly, no maintenance is necessary after major earthquakes for restoring the frame structure.

However, the post-tensioned steel bar needs to pass through the long column of the civil engineering construction. This self-centering mechanism is completely a new approach for upgrading the seismic design of bridge structures. Rather, it is difficult to apply it in the bridge structures which have already been constructed. Accordingly, the applicability of this design approach requires a re-construct of new bridge structures.

SUMMARY OF THE INVENTION

In view of the above, one of objects of the present invention is to provide a compact self-centering damper unit which can solve the problems described above, by generating a self-centering mechanism within the damper unit itself.

Specifically, the compact self-centering damper unit (hereinafter, referred to as “a present damper unit”) according to the present invention is applicable to infrastructures including bridges, railway bridges, buildings, and so on, for seismic energy dissipation.

The present damper unit comprises, a lower beam, an upper beam, a left column, a right column, energy dissipating means, at least a left post-tensioned steel bar, and at least a right post-tensioned steel bar.

The lower beam and the upper beam are disposed in parallel with each other, in such a manner that the upper beam opposes to the lower beam at a position apart from the lower beam.

The left column is interposed between the lower beam and the upper beam at a left side of “the lower beam and the upper beam”, so as to support the upper beam with respect to the lower beam.

The right column is interposed between the lower beam and the upper beam at a right side of “the lower beam and the upper beam”, so as to support the upper beam with respect to the lower beam.

The energy dissipating means is disposed in a frame which is configured by the lower beam, the upper beam, the left column, and the right column. The energy dissipating means dissipates the energy transmitted to the frame, when earthquake occurs.

An upper end of the left post-tensioned steel bar is connected with the upper beam at a position close to the left column. A lower end of the left post-tensioned steel bar is connected with the lower beam at a position close to the left column.

An upper end of the right post-tensioned steel bar is connected with the upper beam at a position close to the right column. A lower end of the right post-tensioned steel bar is connected with the lower beam at a position close to the right column.

The left post-tensioned steel bar may be inserted in the left column. Alternatively, the damper unit may comprise a pair of the left post-tensioned steel bars which are connected through the upper and lower beams. The left post-tensioned steel bars are apart from the left column at a same distance so as not to interfere with energy dissipating means (e.g., dampers) during its movement.

The right post-tensioned steel bar may be inserted in the right column. Alternatively, the damper unit may comprise a pair of the right post-tensioned steel bars which are connected through the upper and lower beams. The right post-tensioned steel bars are apart from the left column at a same distance so as not to interfere with the energy dissipating means during its movement.

More specifically, the left column is semi-rigid connected with “the upper beam and the lower beam” by a compressive force generated by the left post-tensioned steel bar. The right column is semi-rigid connected with “the upper beam and the lower beam” by a compressive force generated by the right post-tensioned steel bar.

The present damper unit having the configuration described above keeps in its original position, when no earthquake occurs.

When earthquake occurs, a conjugate shear forces acts through the upper beam and the lower beam. The left column can be subjected to the bending and rotate relatively with respect to the upper and lower beams. This is due to the semi-rigid connections between the left column and the upper beam as well as between the left column and the lower beam. At the same time, the right column can also act in a way similar to that of the left column. In the meantime, the left column keeps in partially contact with the upper and lower beams due to a compressive force generated from (by) the left post-tensioned steel bar, and the right column also keeps in partially contact with the upper and lower beams due to similar mechanism generated from (by) the right post-tensioned steel bar.

Furthermore, when earthquake occurs, the beams of the semi rigid frame relatively slide following with each other. The energy dissipating means goes to large plastic deformation and dissipates considerable amount of seismic energy. On the other hand, both of the left and the right post-tensioned steel bar are extended. However, these bars possess a mechanism that helps to return to their original positions and to shorten their extended lengths. Consequently, after earthquakes, a residual displacement retained in the present damper unit is recovered. This is because the present damper unit returns to its original position. In other words, as the present damper unit exhibits the self-centering mechanism, no maintenance is required for restoring the frame and/or replacing the present damper unit with a new one, after major earthquakes.

One of aspects of the present invention, it is preferable that,

at least one end portion of “an upper end portion of the left column, a lower end portion of the left column, an upper end portion of the right column, and a lower end portion of the right column” have a rounded convex shape, and

at least one contact portion, which contacts with the at least one end portion having the rounded convex shape, of “a left upper contact portion of the upper beam, a left lower contact portion of the lower beam, a right upper contact portion of the upper beam, and a right lower contact portion of the lower beam” have a rounded concave shape.

More specifically,

the rounded convex shape may preferably be substantially a part of a hemispherical shape having a first predetermined radius; and

the rounded concave shape may preferably be substantially a part of a hemispherical shape having a second predetermined radius larger than the first predetermined radius.

Alternatively,

the rounded convex shape may preferably be substantially a part of a sidewall of a cylinder having a third predetermined radius; and

the rounded concave shape may preferably be substantially a part of a sidewall of a cylinder having a fourth predetermined radius larger than the third predetermined radius.

These features allow the left and right columns to rotatably move more smoothly relative to the upper and lower beams.

Another aspect of the present invention, it is preferable that,

at least one end portion of “an upper end portion of the left column, a lower end portion of the left column, an upper end portion of the right column, and a lower end portion of the right column” may be flat, and

at least one contact portion of “the left upper contact portion of the upper beam, the left lower contact portion of the lower beam, the right upper contact portion of the upper beam, and the right lower contact portion of the lower beam”, the at least one contact portion contacting with the at least one end portion which is flat, have a concave shape substantially having a part of a rectangular parallelepiped.

This aspect enhances the self-centering mechanism of the present damper unit. The reasons behind it are described later.

The energy dissipating means may comprise a first axially yielding damper and a second axially yielding damper.

In this case,

one end of the first axially yielding damper is connected with either the upper beam at the left side or the left column at a position close to an upper end of the left column;

the other end of the first axially yielding damper is connected with either the lower beam at the right side or the right column at a position close to a lower end of the right column;

one end of the second axially yielding damper is connected with either the upper beam at the right side or the right column at a position close to an upper end of the right column; and

the other end of the second axially yielding damper is connected with either the lower beam at the left side or the left column at a position close to a lower end of the left column.

Alternatively, the energy dissipating means may comprise a shear panel which is supported by the frame in such a manner that the shear panel is deformed when the frame is displaced by the seismic force.

In this case, it is preferable that the shear panel has a planar shape being substantially the same rectangular shape as a shape defined by an inside portion of the frame, and four corners of the shear panel are cut out. This feature allows the shear panel to deform more smoothly because the shear panel has cut out potions, as described later in more details.

The present damper unit may include various aspects in addition to the aspects described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Various other objects, features and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description of the preferred embodiments when considered in connection with the accompanying drawings, in which:

FIG. 1 is a schematic view of an arch bridge and a self-centering compact damper unit, according to a first embodiment of the present invention, applied to the arch bridge;

FIG. 2 is a schematic front view of the self-centering compact damper unit shown in FIG. 1;

FIG. 3 is a plan view of the upper beam shown in FIG. 2;

FIG. 4 is a plan view of the lower beam shown in FIG. 2;

FIG. 5 is a schematic front view of the self-centering compact damper unit shown in FIG. 2, when it is at its original position;

FIG. 6 is a schematic front view of the self-centering compact damper unit shown in FIG. 2, when it is subjected to a shearing force;

FIG. 7 is another schematic front view of the self-centering compact damper unit shown in FIG. 2, when it is subjected to a shearing force from reverse direction according to FIG. 6;

FIG. 8 is a schematic front view of the self-centering compact damper unit according to a second embodiment of the present invention;

FIG. 9 is a fragmentary cross-sectional view of the lower beam and the shear panel shown in FIG. 8;

FIG. 10 is a schematic front view of the self-centering compact damper unit shown in FIG. 8, when it is at its original position;

FIG. 11 is a schematic front view of the self-centering compact damper unit shown in FIG. 8, when it is subjected to a shearing force;

FIG. 12 is another schematic front view of the self-centering compact damper unit shown in FIG. 8, when it is subjected to a shearing force from reverse direction according to FIG. 11;

FIG. 13 is a schematic perspective view of the lower beam shown in FIG. 2;

FIG. 14 is a schematic perspective view of a modification of the lower beam shown in FIG. 2;

FIG. 15 is a schematic fragmentary perspective view of a modification of the left column shown in FIG. 2;

FIG. 16 is a schematic perspective view of another modification of the lower beam shown in FIG. 2;

FIG. 17 is a schematic fragmentary perspective view of another modification of the left column shown in FIG. 2;

FIG. 18 is a view for explaining an operation of the modification shown in FIGS. 16 and 17;

FIG. 19 is a schematic front view of an another modification of the self-centering compact damper unit shown in FIG. 2;

FIG. 20 is a schematic front view of a still another modification of the self-centering compact damper unit shown in FIG. 2;

FIG. 21 is a plan view of the upper beam of a modified embodiment;

FIG. 22 is a plan view of the lower beam of a modified embodiment;

FIG. 23 is a schematic view showing a shape of a modified nut; and

FIG. 24 is a schematic view of a truss bridge and the application of self-centering compact damper unit of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next will be described embodiments of a self-centering compact damper unit (hereinafter, referred to as “a present damper unit”) according to the present invention, with reference to the drawings. The present damper unit is applicable to (civil engineering) infrastructures, such as a bridge, an elevated highway, and a building.

First Embodiment

FIG. 1 shows an example of an application of the self-centering compact damper unit 10 (hereinafter, referred to as “a first damper unit 10”) according to a first embodiment of the present damper unit. In the example, the first damper unit 10 is applied to an arch bridge BR.

The first damper unit 10 is disposed among bridge members 1, 2, and 3. A lower portion of the first damper unit 10 is rigidly connected with the arch bridge member 1. An upper portion of the first damper unit 10 is rigidly connected with the bridge members 2 and 3. The seismic force is transmitted through the arch bridge members 1, 2, and 3 to the first damper unit 10. It should be noted that, in a conventional bridge in which the first damper unit 10 is not used, the bridge members 2 and 3 are rigidly connected with the bridge member 1 directly.

As shown in FIGS. 2, 3, and 4, the first damper unit 10 comprises a lower beam 11, an upper beam 12, a left column 21, a right column 22, a left post-tensioned steel bar 31, a right post-tensioned steel bar 32, a first axially yielding damper 41, and a second axially yielding damper 42. The lower beam 11, the upper beam 12, the left column 21, and the right column 22 construct a semi rigid frame.

The lower beam 11 has a substantially rectangular parallelepiped shape. In this example, the lower beam 11 is a hollow quadrangular shape, made of a thick steel plate. The lower beam 11 has a relatively high rigidity and high strength. Alternatively, the lower beam 11 may be a solid bar having the parallelepiped shape. The lower beam 11 may be made of a material other than steel.

As described before, the lower beam 11 is rigidly connected with one of the bridge members, so that a lower surface 11LS of the lower beam 11 contacts with a surface of one of the bridge member. Accordingly, the lower surface 11LS is preferably flat. The lower beam 11 may have flange portions 11 a, 11 a at both ends. Each of the flange portions 11 a has thorough holes H through which bolts can penetrate. The lower beam 11 may be connected with the one of the bridge members by the bolts penetrating the through holes H and nuts. The lower beam 11 may be rigidly connected with the one of the bridge members by connecting means other than the bolts and the nuts.

As shown in FIGS. 2 and 4, the lower beam 11 includes a left lower contact portion 11 b and a right lower contact portion 11 c.

The left lower contact portion 11 b is provided at a left side of the lower beam 11 (i.e., at a position close to a left end of the lower beam 11). The left lower contact portion 11 b is provided on an upper surface 11US of the lower beam 11. The left lower contact' portion 11 b has a rounded concave shape. More specifically, the rounded concave shape of the left lower contact portion 11 b is a part of a substantially hemispherical shape.

The right lower contact portion 11 c is provided at a right side of the lower beam 11 (i.e., at a position close to a right end of the lower beam 11). The right lower contact portion 11 c is provided on the upper surface 11US of the lower beam 11. The right lower contact portion 11 c has a rounded concave shape which is the same as the rounded concave shape of the left lower contact portion 11 b. That is, the shape of the right lower contact portion 11 c is the part of the substantially hemispherical shape.

The lower beam 11 further includes a left lower connecting portion 11 d and a right lower connecting portion 11 e.

The left lower connecting portion 11 d is provided at the left side of the lower beam 11 (i.e., at a position close to the left end of the lower beam 11), and at the lower surface 11LS. The left lower connecting portion 11 d is a concave having a shape which is a substantially rectangular parallelepiped. A thorough hole Ha is provided between (a bottom of) the left lower contact portion 11 b and the left lower connecting portion 11 d.

The right lower connecting portion 11 e is provided at the right side of the lower beam 11 (i.e., at a position close to the right end of the lower beam 11), and at the lower surface 11LS. The right lower connecting portion 11 e is a concave having the same shape as the left lower connecting portion 11 d. A thorough hole Hb is provided between (a bottom of) the right lower contact portion 11 c and the right lower connecting portion 11 e.

The lower beam 11 further includes a left bracket portion 11 f and a right bracket portion 11 g.

The left bracket portion 11 f is provided at the left side of the lower beam 11 (i.e., at a position close to the left lower contact portion 11 b). As shown in FIG. 4, the left bracket portion 11 f is a convex provided on a longer rear side wall 11RR of the lower beam 11 to project to an inside of the lower beam 11. The left bracket portion 11 f has a flat portion which is in parallel with the longer rear side wall 11RR. The flat portion has a hole for a pin.

The right bracket portion 11 g is provided at the right side of the lower beam 11 (i.e., at a position close to the right lower contact portion 11 c). As shown in FIG. 4, the right bracket portion 11 g is a convex provided on a longer front side wall 11FR of the lower beam 11 opposing to and in parallel with the longer rear side wall 11RR on which the left bracket portion 11 f is provided. The right bracket portion 11 g has the same shape as the left bracket portion 11 f. The right bracket portion 11 g thus projects to the inside of the lower beam 11, and has a flat portion which is in parallel with the longer front side wall 11FR. The flat portion has a hole for a pin.

The upper beam 12 has a substantially rectangular parallelepiped shape. The size of the upper beam 12 is roughly equal to the size of the lower beam 11. The upper beam 12 is disposed in parallel with the lower beam 11 at a position apart from the lower beam 11, in such a manner that the upper beam 12 opposes to the lower beam 11.

In this example, the upper beam 12 is a hollow quadrangular shape, made of a thick steel plate. The upper beam 12 has a relatively high rigidity and high strength. Alternatively, the upper beam 12 may be a solid bar having the parallelepiped shape. The upper beam 12 may be made of a material other than steel.

On the upper surface 12US of the upper beam 12, a plate 12 a is rigidly attached to the upper beam 12. The plate 12 a has a plurality holes through which bolts can penetrate. As described before, the upper beam 12 is rigidly connected with the bridge members by the plate 12 a, the bolts and nuts.

As shown in FIGS. 2 and 3, the upper beam 12 includes a left upper contact portion 12 b and a right upper contact portion 12 c.

The left upper contact portion 12 b is provided at a left side of the upper beam 12 (i.e., at a position close to a left end of the upper beam 12). The left upper contact portion 12 b has a rounded concave shape and is provided on a lower surface 12LS of the upper beam 12. More specifically, the rounded concave shape of the left upper contact portion 12 b is a part of a substantially hemispherical shape. In this example., the shape of the left upper contact portion 12 b is the same shape as the left lower contact portion 11 b. The left upper contact portion 12 b is positioned so as to oppose to the left lower contact portion 11 b.

The right upper contact portion 12 c is provided at a right side of the upper beam 12 (i.e., at a position close to a right end of the upper beam 12). The right upper contact portion 12 c has a rounded concave shape which is the same as the rounded concave shape of the left upper contact portion 12 b. That is, the shape of the right upper contact portion 12 c is the part of the substantially hemispherical shape. The right upper contact portion 12 c is provided on the lower surface 12LS of the upper beam 12. In this example, the shape of the right upper contact portion 12 c is the same shape as the right lower contact portion 11 c. The right upper contact portion 12 c is positioned so as to oppose to the right lower contact portion 11 c.

As described above, all of the left lower contact portion 11 b, the right lower contact portion 11 c, the left upper contact portion 12 b, and the right upper contact portion 12 c are the same to each other in shape. A radius of each of the shapes (substantially hemispherical shapes) of those contact portions is referred to as “a second predetermined radius R2”, for convenience (refer to FIG. 13).

The upper beam 12 further includes a left bracket portion 12 d and a right bracket portion 12 e.

The left bracket portion 12 d is provided at the left side of the upper beam 12 (i.e., at a position close to the left upper contact portion 12 b). As shown in FIG. 3, the left bracket portion 12 d is a convex provided on a longer front side wall 12FR of the upper beam 12 to project to an inside of the upper beam 12. The left bracket portion 12 d has a flat portion which is in parallel with the longer front side wall 12FR. The flat portion has a hole for a pin.

The right bracket portion 12 e is provided at the right side of the upper beam 12 (i.e., at a position close to the right upper contact portion 12 c). The right bracket portion 12 e is a convex provided on a longer rear side wall 12RR of the upper beam 12 opposing to and in parallel with the longer front side wall 12FR on which the left bracket portion 12 d is provided. The right bracket portion 12 e has the same shape as the left bracket portion 12 d. The right bracket portion 12 e thus projects to the inside of the upper beam 12, and has a flat portion in parallel with the longer rear side wall 12RR. The flat portion has a hole for a pin.

The left column 21 has a substantially cylindrical shape. The left column 21 is solid and has a thorough hole He extending along a longitudinal axis of the left column 21. In this example, the left column 21 is made of steel. The left column 21 has relatively high rigidity and high strength. The left column 21 may be made of a material other than steel.

The left column 21 is interposed between the lower beam 11 and the upper beam 12 at the left side of the lower beam 11 and the upper beam 12, so as to support the upper beam 12 with respect to the lower beam 11. As described later in detail, the left column 21 is semi-rigid connected with the upper beam 12 and the lower beam 11 by a compressive force generated by the left post-tensioned steel bar 31.

An upper end portion 21 a of the left column 21 has a rounded convex shape. More specifically, the shape of the upper end portion 21 a is a part of (an all of, in this example) a substantially hemispherical shape having a first radius r1. The first radius r1 is smaller than a radius of the left upper contact portion 12 b of the upper beam 12. The upper end portion 21 a coaxially contacts with (a surface of) the left upper contact portion 12 b of the upper beam 12, when the frame is in an original position.

A lower end portion 21 b of the left column 21 has a rounded convex shape. More specifically, the shape of the lower end portion 21 b is a part of (an all of, in this example) a substantially hemispherical shape having a second radius r2. The second radius r2 is smaller than a radius of the left lower contact portion 11 b of the lower beam 11. In this example, the shape of the lower end portion 21 b is the same as the shape of the upper end portion 21 a (r1=r2). The lower end portion 21 b coaxially contacts with (a surface of) the left lower contact portion 11 b of the lower beam 11, when the frame is in the original position.

The right column 22 is the same as the left column 21. That is, the right column 22 has a substantially cylindrical shape which is the same as the shape of the left column 21. The right column 22 is solid and has a thorough hole Hf extending along a longitudinal axis of the right column 22. In this example, the right column 22 is made of steel. The right column 22 has relatively high rigidity and high strength. The right column 22 may be made of a material other than steel.

The right column 22 is interposed between the lower beam 11 and the upper beam 12 at the right side of the lower beam 11 and the upper beam 12, so as to support the upper beam 12 with respect to the lower beam 11. As described later in detail, the right column 22 is semi-rigid connected with the upper beam 12 and the lower beam 11 by a compressive force generated by the right post-tensioned steel bar 32.

An upper end portion 22 a of the right column 22 has a rounded convex shape. More specifically, the shape of the upper end portion 22 a is a part of (an all of, in this example) a substantially hemispherical shape having a third radius r3. The third radius r3 is smaller than a radius of the right upper contact portion 12 c of the upper beam 12. The shape of the upper end portion 22 a is also the same as the shape of the upper end portion 21 a. The upper end portion 22 a coaxially contacts with (a surface of) the right upper contact portion 12 c of the upper beam 12, when the frame is in the original position.

A lower end portion 22 b of the right column 22 has a rounded convex shape. More specifically, the shape of the lower end portion 22 b is a part of (an all of, in this example) a substantially hemispherical shape having a fourth radius r4. The fourth radius r4 is smaller than a radius of the right lower contact portion 11 c of the lower beam 11. The shape of the lower end portion 22 b is the same as the shape of the upper end portion 22 a (r3=r4). The shape of the lower end portion 22 b is also the same as the shape of the lower end portion 21 b. The lower end portion 22 b coaxially contacts with (a surface of) the right lower contact portion 11 c of the lower beam 11, when the frame is in the original position.

As described above, any one of the upper end portion 21 a, the lower end portion 21 b, the upper end portion 22 a, and the lower end portion 22 b have the same shape. The radii r1, r2, r3, and r4 are therefore the same to each other. Each of the radii r1, r2, r3, and r4 is referred to as “a first predetermined radius R1, for convenience. The second predetermined radius R2 described above is larger than the first predetermined radius R1.

The left post-tensioned steel bar 31 passes through the left column 21 along the longitudinal axis of the left column 21. That is, the left post-tensioned steel bar 31 passes through the hole He of the left column 21 (the steel bar 31 is inserted in the left column 21). The clear space between the left post-tensioned steel bar 31 and the hole He is sufficient in order not to restrain the movement of steel bar 31. The left post-tensioned steel bar 31 further passes through the lower beam 11. That is, the left post-tensioned steel bar 31 passes through the hole Ha of the lower beam 11. The left post-tensioned steel bar 31 further passes through the upper beam 12. That is, the left post-tensioned steel bar 31 passes through the hole Hc of the upper beam 12. The clear spaces between the left post-tensioned steel bar 31 and the hole Ha as well as between the left post-tensioned steel bar 31 and the hole Hc are sufficient in order not to restrain the movement of steel bar 31. That is, the steel bar 31 does not contact with sidewalls of the holes Ha and Hc.

An upper end 31 a of the left post-tensioned steel bar 31 projects from an upper surface 12US of the upper beam 12, as shown in FIG. 2. A bolt thread is formed on the upper end 31 a. A nut N1 is screwed onto the bolt thread.

A lower end 31 b of the left post-tensioned steel bar 31 projects into the left lower connecting portion 11 d, as shown in FIG. 2. A bolt thread is formed on the lower end 31 b. A nut N2 is screwed onto the bolt thread.

The nut N1 and the nut N2 are screwed so that a tension (tension force) is provided to the left post-tensioned steel bar 31. Accordingly, the left column 21 is semi-rigid connected with the upper beam 12 and the lower beam 11 by a compressive force generated by the left post-tensioned steel bar 31.

The right post-tensioned steel bar 32 passes through the right column 22 along the longitudinal axis of the right column 22. That is, the right post-tensioned steel bar 32 passes through the hole Hf of the right column 22. (the steel bar 32 is inserted in the right column 22). The clear space between the right post-tensioned steel bar 32 and the hole Hf is sufficient in order not to restrain the movement of steel bar 32. The right post-tensioned steel bar 32 further passes through the lower beam 11. That is, the right post-tensioned steel bar 32 passes through the hole Hb of the lower beam 11 (the steel bar 32 is inserted in the right column 22). The right post-tensioned steel bar 32 further passes through the upper beam 12. That is, the right post-tensioned steel bar 32 passes through the hole Hd of the upper beam 12. The clear spaces between the right post-tensioned steel bar 32 and the hole Hb as well as the right post-tensioned steel bar 32 and the hole Hd are sufficient in order not to restrain the movement of steel bar 32. That is, the steel bar 32 does not contact with sidewalls of the holes Hb and Hd.

An upper end 32 a of the right post-tensioned steel bar 32 projects from the upper surface 12US of the upper beam 12, as shown in FIG. 2. A bolt thread is formed on the upper end 32 a. A nut N3 is screwed onto the bolt thread.

A lower end 32 b of the right post-tensioned steel bar 32 projects into the right lower connecting portion 11 e, as shown in FIG. 2. A bolt thread is formed on the lower end 32 b. A nut N4 is screwed onto the bolt thread.

The nut N3 and the nut N4 are screwed so that a tension (tension force) is provided to the right post-tensioned steel bar 32. Accordingly, the right column 22 is semi-rigid connected with the upper beam 12 and the lower beam 11 by a compressive force generated by the right post-tensioned steel bar 32.

The first axially yielding damper 41 is a well known damper. An upper end of the first axially yielding damper 41 is pin-connected with the upper beam 12 at the left bracket portion 12 d. A lower end of the first axially yielding damper 41 is pin-connected with the lower beam 11 at the right bracket portion 11 g.

The second axially yielding damper 42 is the same as the first axially yielding damper 41. An upper end of the second axially yielding damper 42 is pin-connected with the upper beam 12 at the right bracket portion 12 e. A lower end of the second axially yielding damper 42 is pin-connected with the lower beam 11 at the left bracket portion 11 f.

Accordingly, the first axially yielding damper 41 is disposed in such a manner that the first axially yielding damper 41 substantially connects one pair of diagonal corners of the frame. The second axially yielding damper 42 is disposed in such a manner that the second axially yielding damper 42 substantially connects the other one pair of diagonal corners of the frame.

That is, the first axially yielding damper 41 and the second axially yielding damper 42 constitute energy dissipating means, which is disposed in the frame configured by the lower beam 11, the upper beam 12, the left column 21, and the right column 22, for dissipating (absorbing) seismic energy applied to the frame.

Next will be described the mechanism of the first damper unit 10, with reference to FIGS. 5, 6, and 7. It should be noted that the first damper unit 10 is schematically shown in FIGS. 5, 6, and 7.

When no earthquake occurs, the first damper unit 10 (the frame) maintains its original shape (position) as shown in FIG. 5.

When earthquake occurs, a force is applied to the first damper unit 10 (the frame) through the bridge members connected with the first damper unit 10.

FIG. 6 shows a case in which a force F1 in a right direction is applied to the upper beam 12 through the bridge members, and a force F2 in a left direction is applied to the lower beam 11 through the bridge members.

In this case, the left column 21 keeps in partially contact with the upper beam 12 and the lower beam 11 owing to the compressive force provided by the left post-tensioned steel bar 31. However, the left column 21 is rotatably movable with respect to the upper beam 12 and the lower beam 11, owing to the semi-rigid connection between the left column 21 and the upper beam 12 as well as the semi-rigid connection between the left column 21 and the lower beam 11.

Furthermore, as described above, the first radius r1 is smaller than a radius of the left upper contact portion 12 b, and the second radius r2 is smaller than a radius of the left lower contact portion 11 b (refer to FIG. 2). Therefore, the left column 21 can rotatably move with respect to the lower beams 11 and the upper beam 12 smoothly, with contacting with these beams.

Similarly, the right column 22 keeps in partially contact with the upper beam 12 and the lower beam 11 owing to the compressive force generated by the right post-tensioned steel bar 32. However, the right column 22 is rotatably movable with respect to the upper beam 12 and the lower beam 11, owing to the semi-rigid connection between the right column 22 and the upper beam 12 as well as the semi-rigid connection between the right column 22 and the lower beam 11.

Furthermore, as described above, the third radius r3 is smaller than a radius of the right upper contact portion 12 c, and the fourth radius r4 is smaller than a radius of the right lower contact portion 11 c (refer to FIG. 2). Therefore, the right column 22 can rotatably move with respect to the lower beams 11 and the upper beam 12 smoothly, with contacting with these beams.

Accordingly, as shown in FIG. 6, when the relative rotation and gap occur between the beam-column connections, the first axially yielding damper 41 goes into compression, where as second axially yielding damper 42 goes into tension. Therefore, the energy is dissipated significantly by both of the axially yielding dampers 41, 42.

At the same time, both of the left post-tensioned steel bar 31 and the right post-tensioned steel bar 32 are extended. However, both of the post-tensioned steel bars 31, 32 are pre-stressed. Therefore, a compressive force is developed within both steel bars 31, 32 which enforces them to return to their original positions and shortens their extended lengths as well.

The residual displacement of retained in both axially yielding dampers 41, 42 is recovered. This is because the first damper unit 10 returns to its original position at each cycle of the earthquake loading history, which is schematically shown in FIG. 5. On the other hand, the first damper unit 10 exhibits the self-centering mechanism. Therefore, no maintenance is necessary for restoring the frame and/or replacing the first damper unit 10 with a new one. Alternatively, it can be said that the first damper unit 10 is maintenance-free after major earthquakes.

FIG. 7 shows a case in which a conjugate of shear forces F3 and F4 acts in the respective beams in a direction reverse to that of F1 and F2. In this case, the first damper unit 10 acts in a way similar to that of the case shown in FIG. 6.

That is, the second axially yielding damper 42 is compressed, where as the first axially yielding damper 41 is extended. Thereby, both of the axially yielding dampers 41, 42 go to the large plastic deformation and dissipate considerable amount of seismic energy.

Simultaneously, both of the left post-tensioned steel bar 31 and the right post-tensioned steel bar 32 also exhibit a mechanism similar to the case shown in FIG. 6. In this way, the first damper unit 10 possesses both the self-centering and the energy dissipation characteristics. Further, the residual displacement retained within both of axially yielding dampers 41, 42 is recovered due to self-centering mechanism of the first damper unit 10, even though both of the dampers 41, 42 go to large plastic deformation.

Second Embodiment

FIG. 8 shows a self-centering compact damper unit 50 (hereinafter, referred to as “a second damper unit 50”) according to a second embodiment of the present invention. The second damper unit 50 can also be applied to the arch bridge BR or other structures, similarly to the first damper unit 10.

The second damper unit 50 is different from the first damper unit 10 only in that the second damper unit 50 comprises a shear panel 60, in place of the first and second axially yielding dampers 41, 42, as an energy dissipating means.

The shear panel 60 has a substantially rectangular shape. More specifically, the shear panel 60 has a planar shape which is substantially the same rectangular shape as a shape defined by an inside portion of the frame. Four corners of the shear panel 60 are cut out. A shape of each of the cut-out portions 61-64 is substantially a quarter circle, but may be another shape including a triangle.

The shear panel 60 is disposed in the frame, and is supported by the frame in such a manner that the shear panel 60 is deformed when the frame members (beams) relatively slide due to shearing action. More specifically, as shown in FIG. 9, two connecting means (top-seat-angle) 11 h are rigidly connected to the upper surface 11US of the lower beam 11. The shear panel 60 is sandwiched between two top-seat-angles, and connected to the lower beam 11 through bolts and nuts which pass through two top-seat angles and the shear panel 60. The shear panel 60 is also rigidly connected to the upper beam 12, the left column 21 and the right column 22, in the same manner. The shear panel 60 may be rigidly connected with the lower beam 11 and the upper beam 12, the left column 21 and the right column 22 in a different manner.

As shown in FIGS. 10, 11, and 12, the second damper unit 50 acts in the way similar to that of the first damper unit 10. Accordingly, the seismic energy is dissipated by the shear panel 60, functioning as the energy dissipating means.

Further, when the frame is displaced under shearing action, the left post-tensioned steel bar 31 and the right post-tensioned steel bar 32 return to their original position at which each of the length of the left post-tensioned steel bar 31 and the right post-tensioned steel bar 32 becomes shortest. As a result, the residual displacement of the shear panel 60 is recovered. In other words, the second damper unit 50 also exhibits the self-centering mechanism. Accordingly, no maintenance is necessary for restoring the frame and/or replacing the second damper unit 50 with a new one.

Furthermore, the shear panel 60 having the cut-out portions 61-64 can deform smoothly. This is because the frame does not restrain the deformation of the shear panel when the frame is displaced by the seismic force.

The present invention is not limited to the embodiments described above, but may be modified as appropriate without departing from the scope of the invention.

For example, in the embodiments described above, each of the left lower contact portion 11 b, the right lower contact portion 11 c, the left upper contact portion 12 b, and the right upper contact portion 12 c has the rounded concave shape which is the part of a substantially hemispherical shape, as shown in FIG. 13. However, as shown in FIG. 14, at least any one of the left lower contact portion 11 b, the right lower contact portion 11 c, the left upper contact portion 12 b, and the right upper contact portion 12 c may have a rounded concave shape which is substantially a part of sidewall of a cylinder whose radius is a fourth predetermined radius R4. That is, at least one of the contact portions may have a shape of the sidewall of a barrel, or be hog-backed.

In this case, as shown in FIG. 15, one of the lower end portion 21 b of the left column 21, the upper end portion 21 a of the left column 21, the lower end portion 22 b of the right column 22, and the upper end portion 22 a of the right column 22, which contacts with one of the contact portions substantially having the shape of the part of cylinder sidewall, has a shape substantially having a shape of the sidewall of a cylinder whose radius is a third predetermined radius R3 smaller than the fourth predetermined radius R4. This configuration can also allow the columns (21 & 22) to move rotatably and smoothly.

Further, as shown in FIG. 16, at least any one of the left lower contact portion 11 b, the right lower contact portion 11 c, the left upper contact portion 12 b, and the right upper contact portion 12 c may have a concave shape having a part of a substantially rectangular parallelepiped. In this case, as shown in FIG. 17, one of the lower end portion 21 b of the left column 21, the upper end portion 21 a of the left column 21, the lower end portion 22 b of the right column 22, and the upper end portion 22 a of the right column 22, which contacts with one of the contact portions having the shape of the part of a substantially rectangular-parallelepiped, has a flat end portions. In other words, each shape of the left column 22 and the right column 22 may be the rectangular parallelepiped, if all of the left lower contact portion 11 b, the right lower contact portion 11 c, the left upper contact portion 12 b, and the right upper contact portion 12 c have the shape of a rectangular parallelepiped.

According to the configuration described above, as shown in FIG. 18, a distance D becomes larger, when the column 21 (or the column 22) is uplifted due to the shear displacement of the frame caused by the seismic energy. The compressive force developed in the post-tensioned steel bar 31 (or the post-tensioned steel bar 32) becomes large as it is extended more effectively. As a result, the self-centering mechanism of damper unit is enhanced.

Further, as shown in FIGS. 19 and 20, at least one of end of the first axially yielding damper 41 may be pin connected with either the left column 21 or the right column 22, and at least one of end of the second axially yielding damper 42 may be pin connected with either the left column 21 or the right column 22. Both ends of the axially yielding dampers may be connected with left column 21 or right column 22 in a different manner.

Further, the first axially yielding damper 41, the second axially yielding damper 42, and the shear panel 60 may be used together in one of the present damper unit.

Furthermore, as shown in FIGS. 21 and 22, a pair of left post-tensioned steel bars 101 a, 101 b may be used in place of the left post-tensioned steel bar 31. The pair of left post-tensioned steel bars 101 a, 101 b are connected through the upper and lower beams 12, 11 to the upper and lower beams 12, 11. The pair of left post-tensioned steel bars 101 a, 101 b are apart from the left column 21 at a same distance and do not interfere with the damper (41, 42, 60) during its movement.

More specifically, in this modification, the pair of left post-tensioned steel bars 101 a, 101 b are placed at symmetrical positions with respect to the left column 21, and are not inserted in the left column 21. A straight line SL1 passing through center axes of the pair of left post-tensioned steel bars 101 a, 101 b is perpendicular to a straight line SL2 passing through the center axes of the left column 21 and the right column 22, when the frame is in the original position.

One end of the steel bar 101 a passes through a hole provided in the upper beam 12, and is connected with the upper beam 12 by a nut N1 a which is screwed onto a bolt thread of the steel bar 101 a. Similarly, the other end of the steel bar 101 a passes through a hole provided in the lower beam 11, and is connected with the lower beam 11 by a nut N2 a which is screwed onto a bolt thread of the steel bar 101 a. The nut N1 a and the nut N2 a are screwed so that a tension (tension force) is provided to the left post-tensioned steel bar 101 a. The other steel bar 101 b is connected with the upper and lower beams 12, 11, in the same way that the steel bar 101 a is connected with the upper and lower beams 12, 11.

Accordingly, the left column 21 is semi-rigid connected with the upper beam 12 and the lower beam 11 by a compressive force generated by the pair of the left post-tensioned steel bars 101 a, 101 b.

Similarly, as shown in FIGS. 21 and 22, a pair of right post-tensioned steel bars 102 a, 102 b may be used in place of the right post-tensioned steel bar 32. The pair of right post-tensioned steel bars 102 a, 102 b are connected through the upper and lower beams 12, 11 to the upper and lower beams. The pair of right post-tensioned steel bars 102 a, 102 b are apart from the right column 21 at a same distance and do not interfere with the damper (41, 42, 60) during its movement.

The pair of right post-tensioned steel bars 102 a, 102 b are placed at symmetrical positions with respect to the right column 22, and are not inserted in the right column 22. A straight line SL3 passing through center axes of the pair of right post-tensioned steel bars 102 a, 102 b is perpendicular to the straight line SL2, when the frame is in the original position. The steel bars 102 a, 102 b are connected with the upper and lower beams 12, 11, in the same way that the steel bar 101 a is connected with the upper and lower beams 12, 11.

Accordingly, the right column 22 is semi-rigid connected with the upper beam 12 and the lower beam 11 by a compressive force generated by the pair of the right post-tensioned steel bars 102 a, 102 b.

Further, as shown in FIG. 23, each of the nuts N1, N2, N3, N4, N1 a, N1 b, N2 a, N2 b, N3 a, N3 b, N4 a, and N4 b may be replaced by a nut Nx having a seating face which is rounded (i.e., a shape of the seating face is a part of a hemispherical shape). This allows the post-tensioned steel bars 31, 32, 101 a, 101 b, 102 a, and 102 b extends more smoothly.

Moreover, as shown in FIG. 24 the present damper can obviously be applied to a truss bridge. 

1. A self-centering compact damper unit applicable to structures for seismic energy dissipation comprising: a lower beam; an upper beam disposed in parallel with and opposing to said lower beam at a position apart from said lower beam; a left column interposed between said lower beam and said upper beam at a left side of said lower beam and said upper beam so as to support said upper beam; a right column interposed between said lower beam and said upper beam at a right side of said lower beam and said upper beam so as to support said upper beam; energy dissipating means, disposed in a frame configured by said lower beam, said upper beam, said left column, and said right column, for dissipating seismic energy applied to said frame; at least a left post-tensioned steel bar, an upper end of said left post-tensioned steel bar being connected with said upper beam at a position close to said left column, and a lower end of said left post-tensioned steel bar being connected with said lower beam at a position close to said left column; and at least a right post-tensioned steel bar, an upper end of said right post-tensioned steel bar being connected with said upper beam at a position close to said right column, and a lower end of said right post-tensioned steel bar is connected with said lower beam at a position close to said right column.
 2. A self-centering compact damper unit according to claim 1, wherein, said left column is semi-rigid connected with said upper beam and said lower beam by a compressive force generated by said left post-tensioned steel bar; and said right column is semi-rigid connected with said upper beam and said lower beam by a compressive force generated by said right post-tensioned steel bar.
 3. A self-centering compact damper unit according to claim 2, wherein, said left post-tensioned steel bar is inserted in said left column, and said right post-tensioned steel bar is inserted in said right column.
 4. A self-centering compact damper unit according to claim 2, comprising: at least a pair of said left post-tensioned steel bars which are apart from said left column at a same distance so as not to interfere with said energy dissipating means during a movement of said energy dissipating means; and at least a pair of said right post-tensioned steel bars which are apart from said right column at a same distance so as not to interfere with said energy dissipating means during a movement of said energy dissipating means.
 5. A self-centering compact damper unit according to claim 2, wherein, at least one end portion of an upper end portion of said left column, a lower end portion of said left column, an upper end portion of said right column, and a lower end portion of said right column has a rounded convex shape, and at least one contact portion of a left upper contact portion of said upper beam, a left lower contact portion of said lower beam, a right upper contact portion of said upper beam, and a right lower contact portion of said lower beam, said at least one contact portion contacting with said at least one end portion, has a rounded concave shape.
 6. A self-centering compact damper unit according to claim 5, wherein, said rounded convex shape is substantially a part of a hemispherical shape having a first predetermined radius; and said rounded concave shape is substantially a part of a hemispherical shape having a second predetermined radius larger than said first predetermined radius.
 7. A self-centering compact damper unit according to claim 5, wherein, said rounded convex shape is substantially a part of a sidewall of a cylinder having a third predetermined radius; and said rounded concave shape is substantially a part of a sidewall of a cylinder having a fourth predetermined radius larger than said third predetermined radius.
 8. A self-centering compact damper unit according to claim 2, wherein, at least one end portion of an upper end portion of said left column, a lower end portion of said left column, an upper end portion of said right column, and a lower end portion of said right column is flat, and at least one contact portion of said left upper contact portion of said upper beam, said left lower contact portion of said lower beam, said right upper contact portion of said upper beam, and said right lower contact portion of said lower beam, said at least one contact portion contacting with said at least one end portion, has a concave shape substantially having a part of a rectangular parallelepiped.
 9. A self-centering compact damper unit according to claim 1, wherein, said energy dissipating means comprises a first axially yielding damper and a second axially yielding damper, one end of said first axially yielding damper is connected with either said upper beam at said left side or said left column at a position close to an upper end of said left column; the other end of said first axially yielding damper is connected with either said lower beam at said right side or said right column at a position close to a lower end of said right column; one end of said second axially yielding damper is connected with either said upper beam at said right side or said right column at a position close to an upper end of said right column; and the other end of said second axially yielding damper is connected with either said lower beam at said left side or said left column at a position close to a lower end of said left column.
 10. A self-centering compact damper unit according to claim 1, wherein, said energy dissipating means comprises a shear panel which is supported by said frame in such a manner that said shear panel is deformed when said frame is deformed by said seismic energy.
 11. A self-centering compact damper unit according to claim 10, wherein, said shear panel has a planar shape being substantially the same rectangular shape as a shape defined by an inside portion of said frame, and four corners of said shear panel are cut out.
 12. A self-centering compact damper unit according to claim 2, wherein said left column comprises an upper end portion having a rounded convex shape and a lower end portion having a rounded convex shape; said right column comprises an upper end portion having a rounded convex shape and a lower end portion having a rounded convex shape; said lower beam comprises a left lower contact portion having a rounded concave shape on an upper surface of said lower beam at said left side, and a right lower contact portion having a rounded concave shape on said upper surface of said lower beam at said right side, said left lower contact portion contacting with said lower end portion of said left column, and said right lower contact portion contacting with said lower end portion of said right column; and said upper beam comprises a left upper contact portion having a rounded concave shape on a lower surface of said upper beam at said left side, and a right upper contact portion having a rounded concave shape on said lower surface of said upper beam at said right side, said left upper contact portion contacting with said upper end portion of said left column, and said right upper contact portion contacting with said upper end portion of said right column.
 13. A self-centering compact damper unit according to claim 12, wherein, said rounded shape of said upper end portion of said left column is a part of a substantially hemispherical shape having a first radius; said rounded shape of said lower end portion of said left column is a part of a substantially hemispherical shape having a second radius; said rounded shape of said upper end portion of said right column is a part of a substantially hemispherical shape having a third radius; said rounded shape of said lower end portion of said right column is a part of a substantially hemispherical shape having a fourth radius; said rounded concave shape of said left upper contact portion of said upper beam is a part of a substantially hemispherical shape having a radius larger than said first radius; said rounded concave shape of said left lower contact portion of said lower beam is a part of a substantially hemispherical shape having a radius larger than said second radius; said rounded concave shape of said right upper contact portion of said upper beam is a part of a substantially hemispherical shape having a radius larger than said third radius; and said rounded concave shape of said right lower contact portion of said lower beam is a part of a substantially hemispherical shape having a radius larger than said fourth radius. 